A hollow ZIF-L framework material and a method for preparing the same

Abstract

The application discloses a kind of hollow ZIF-L frame materials and preparation method thereof.The application uses continuous preparation method to make precursor ZIF material pre-stratification in synthesis system, after removing part supernatant, precursor dispersion liquid is transferred to flat hydrophilic substrate and dried, and a kind of hollow ZIF-L frame material is prepared using Malan Guni effect.The hollow ZIF-L frame material prepared by the method has unique structural characteristics, and can be widely used as a carrier in gas adsorption and separation, drug delivery and electrochemical technology field.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nanomaterials. More particularly, it relates to a hollow ZIF-L framework material and a preparation method thereof. BACKGROUND

[0002] Metal-organic frameworks (MOFs) have attracted extensive interest in the field of materials science due to their unique properties and potential applications. ZIF-L (Zeolitic Imidazolate Framework-L) is a member of the MOFs family, which has a unique structure and diverse application potential. The synthesis of ZIF-L materials usually employs a solution synthesis method, in which metal ions and organic ligands combine under appropriate conditions to form a crystalline structure. Common metal ions include zinc, cobalt, copper, etc., while the organic ligand is usually an imidazole compound, such as 2-methylimidazole. By adjusting the synthesis conditions, ZIF-L crystals of different morphologies and sizes can be achieved to meet various application requirements. One of the most notable features of ZIF-L materials is their porous structure, which is similar to molecular sieves and consists of continuous porous channels that can accommodate various molecules and ions. In addition, ZIF-L crystals have highly controllable pore size and porosity. ZIF-L materials, as a kind of porous crystalline material, have unique structure and wide application potential. They exhibit excellent performance in gas adsorption, catalysis, drug delivery, and energy storage, etc. However, in practical applications, the sheet-like structure of ZIF-L materials is prone to stacking, which loses the advantage of high porosity of ZIF-L materials, resulting in loss of adsorption or carrier performance.

[0003] Therefore, there is a need for a ZIF-L material with a hollow structure that is simple to prepare, to solve the problem of performance loss caused by material stacking in various fields of application. SUMMARY

[0004] In view of the above problems in the prior art, the first object of the present application is to provide a hollow ZIF-L framework material. The hollow ZIF-L framework has a hollow structure, which can avoid stacking and performance loss in application, and provide higher mass transfer capacity. The second object of the present application is to provide a preparation method of a hollow ZIF-L framework material. The method has low cost and forms the target structure by controlling the synthesis conditions.

[0005] To achieve the above-mentioned first object, the present application adopts the following technical solutions:

[0006] A hollow ZIF-L framework material, the material presents a framework morphology with twelve edges connected to form a hollow structure, and each edge is composed of a coordination compound of metal ions and organic ligands.

[0007] To achieve the above-mentioned second object, the application adopts the following technical solutions:

[0008] A preparation method of a hollow ZIF-L framework material, a metal salt and a surfactant are dissolved in water, an organic ligand solution is added, the mixture is uniformly mixed to obtain a precursor reaction solution of the material, supernatant of the precursor reaction solution is removed, the remaining mother liquor is added dropwise on a flat hydrophilic substrate, and the hollow ZIF-L framework material is prepared after drying.

[0009] Preferably, the metal salt is one or both of a cobalt salt or a zinc salt.

[0010] Preferably, the organic ligand is 2-methylimidazole.

[0011] Preferably, the surfactant is cetyltrimethylammonium bromide (CTAB), and the molar ratio of the surfactant to the metal ion is (1:30)~(1:180).

[0012] Preferably, the molar ratio of the metal ion to the organic ligand is (1:30)~(1:70).

[0013] Preferably, the volume of the removed supernatant is 50%-85% of the total volume.

[0014] Preferably, the flat hydrophilic substrate is selected from any one of a silicon wafer, glass, quartz, stainless steel, aluminum alloy and ceramic.

[0015] Compared with the prior art, the application has the beneficial effects that the application provides a hollow ZIF-L framework material, which can effectively avoid the problems of stacking, performance loss and the like of ZIF-L materials. Meanwhile, the application provides a preparation method of a hollow ZIF-L framework material, by adjusting the parameters in the synthesis process of the ZIF material, the ZIF-L precursor is affected by the change of the concentration of the crystallization unit in the synthesis process to change the crystallization habit, dissociate and grow again, and successfully form a hollow framework structure; the preparation method avoids the commonly used etching agent and the complicated pore-forming method, and is economical and efficient; the hollow ZIF-L framework material is prepared through a continuous preparation process, high synthesis efficiency can be obtained, and continuous large-scale production is realized. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 A scanning electron microscope image of the hollow ZIF-L framework material obtained in Example 1 is shown.

[0017] Figure 2 A transmission electron microscope image of the hollow ZIF-L framework material obtained in Example 1 is shown.

[0018] Figure 3An XRD pattern of the hollow ZIF-L framework material obtained in Example 1 is shown.

[0019] Figure 4 A scanning electron microscope pattern of the nanocubes obtained in Comparative Example 1 is shown.

[0020] Figure 5 A scanning electron microscope pattern of the two-dimensional nanosheets obtained in Comparative Example 2 is shown.

[0021] Figure 6 A scanning electron microscope pattern of the two-dimensional nanosheets obtained in Comparative Example 3 is shown. DETAILED DESCRIPTION

[0022] In order to more clearly illustrate the present application, the present application will be further described below in conjunction with preferred embodiments and the accompanying drawings. It should be understood by those skilled in the art that the specific description below is illustrative rather than limiting, and should not limit the scope of protection of the present application.

[0023] Example 1:

[0024] A method for preparing a hollow ZIF-L framework material, comprising the following steps:

[0025] 1 mmol of cobalt nitrate hexahydrate and 0.006 mmol of CTAB were weighed and dissolved in 10 mL of deionized water to obtain solution 1;

[0026] 54 mmol of 2-methylimidazole was weighed and dissolved in 70 mL of deionized water to obtain solution 2;

[0027] Solution 1 was added to solution 2, and stirred for 20 min to obtain a mixed solution 3;

[0028] The mixed solution 3 was left to stand for 24 h, and 70 mL of the upper solution was removed to obtain a mother liquor 4;

[0029] The mother liquor 4 was added dropwise onto a silicon wafer, and dried to obtain a Co-ZIF-L hollow framework material.

[0030] Figure 1 and Figure 2 are scanning electron microscope and transmission electron microscope patterns of the sample obtained in Example 1, respectively, from which Figure 1 and Figure 2 It can be seen that the sample morphology is a framework morphology of a hollow structure composed of twelve edges connected to each other, and each edge is composed of a coordination compound of metal ions and organic ligands, and the morphology is regular and uniformly distributed.

[0031] Figure 3 is an XRD pattern of the sample obtained in Example 1, and from the crystal structure of the sample it can be seen that it is a Co-ZIF-L.

[0032] Example 2

[0033] A method for preparing a hollow ZIF-L framework material, comprising the following steps:

[0034] 1 mmol of zinc nitrate hexahydrate and 0.006 mmol of CTAB were weighed and dissolved in 10 mL of deionized water to obtain solution one;

[0035] 54 mmol of 2-methylimidazole was weighed and dissolved in 70 mL of deionized water to obtain solution two;

[0036] Solution one was added to solution two, and stirred for 20 min to obtain solution three;

[0037] Solution three was left to stand for 24 h, and 70 mL of the upper solution was removed to obtain mother liquor four;

[0038] Mother liquor four was added dropwise to a silicon wafer, and after drying, a Zn-ZIF-L hollow framework material was obtained. Scanning electron microscopy was performed, indicating that the hollow ZIF-L framework material can also be obtained by replacing the metal salt with zinc nitrate hexahydrate. Example 3

[0039] A method for preparing a hollow ZIF-L framework material, comprising the following steps:

[0040] 1) 0.5 mmol of cobalt nitrate hexahydrate, 0.5 mmol of zinc nitrate hexahydrate, and 0.006 mmol of CTAB were weighed and dissolved in 10 mL of deionized water to obtain solution one;

[0041] 2) 54 mmol of 2-methylimidazole was weighed and dissolved in 70 mL of deionized water to obtain solution two;

[0042] 3) Solution one was added to solution two, and stirred for 20 min to obtain solution three;

[0043] 4) Solution three was left to stand for 24 h, and 70 mL of the upper solution was removed to obtain mother liquor four;

[0044] 5) Mother liquor four was added dropwise to a silicon wafer, and after drying, a Co / Zn-ZIF-L hollow framework material was obtained. Scanning electron microscopy was performed, indicating that the hollow ZIF-L framework material can also be obtained by replacing the metal salt with cobalt nitrate hexahydrate and zinc nitrate hexahydrate, each occupying half.

[0045] Comparative Example 1

[0046] 1) 1 mmol of zinc nitrate hexahydrate and 0.006 mmol of CTAB were weighed and dissolved in 10 mL of deionized water to obtain solution one;

[0047] 2) Weigh 54 mmol 2-methylimidazole dissolved in 70 mL deionized water to obtain solution two;

[0048] 3) Add solution one to solution two, stir for 20 min to obtain solution three;

[0049] 4) Let solution three stand for 24 h, remove 70 mL of the upper solution to obtain mother liquor four;

[0050] 5) Centrifuge mother liquor four in a high-speed centrifuge and wash three times with anhydrous ethanol;

[0051] 6) Dry the centrifuged sample in a vacuum drying oven at 60°C for 24 h.

[0052] Figure 4 The scanning electron microscope image of the sample prepared for Comparative Example One can be seen from Figure 4 , and it can be seen that the sample morphology is nanocubes, indicating that the sample prepared by the conventional method can only obtain nanocube morphology and cannot obtain three-dimensional hollow nanoframe morphology.

[0053] Comparative Example Two:

[0054] 1) Weigh 1 mmol zinc nitrate hexahydrate and 0.006 mmol CTAB dissolved in 10 mL deionized water to obtain solution one;

[0055] 2) Weigh 8 mmol 2-methylimidazole dissolved in 70 mL deionized water to obtain solution two;

[0056] 3) Add solution one to solution two, stir for 20 min to obtain solution three;

[0057] 4) Let solution three stand for 24 h, remove 70 mL of the upper solution to obtain mother liquor four;

[0058] 5) Centrifuge mother liquor four in a high-speed centrifuge and wash three times with anhydrous ethanol;

[0059] 6) Dry the centrifuged sample in a vacuum drying oven at 60°C for 24 h.

[0060] Figure 5 The scanning electron microscope image of the sample prepared for Comparative Example Two can be seen from Figure 5 , and it can be seen that the sample morphology is two-dimensional nanosheet, indicating that when the ratio of transition metal salt and ligand is not within the appropriate range, the obtained product is two-dimensional nanosheet morphology instead of nanocube morphology.

[0061] Comparative Example Three:

[0062] 1) Weigh 1 mmol of zinc nitrate hexahydrate and 0.006 mmol of CTAB into 10 mL of deionized water to obtain solution one;

[0063] 2) Weigh 8 mmol of 2-methylimidazole into 70 mL of deionized water to obtain solution two;

[0064] 3) Add solution one into solution two and stir for 20 min to obtain solution three;

[0065] 4) Let solution three stand for 24 h and remove 70 mL of the upper solution to obtain mother liquor four;

[0066] 5) Drop the mother liquor onto a silicon wafer.

[0067] Figure 6 The scanning electron microscope image of the sample prepared for Comparative Example Three can be seen from Figure 6 , and it can be seen that the sample morphology is still two-dimensional nanosheet, which indicates that the ratio of cobalt nitrate hexahydrate and 2-methylimidazole ligand is not within the appropriate range, and the ZIF-L nanoframe with three-dimensional hollow morphology cannot be obtained by dropping onto a silicon wafer.

Claims

1. A method for preparing a hollow ZIF-L framework material, characterized in that, The material presents a frame morphology of twelve edges connected to form a hollow structure, each edge being composed of a coordination compound of metal ions and organic ligands, comprising the following steps: dissolving a metal salt and a surfactant in water, adding an organic ligand solution, uniformly mixing to obtain a precursor reaction solution of the material, removing supernatant of the precursor reaction solution, dropping the remaining mother liquor on a flat hydrophilic substrate, and drying to obtain the hollow ZIF-L frame material; The metal salt is one or both of cobalt salt or zinc salt; The organic ligand is 2-methyl imidazole; The molar ratio of metal ions to organic ligands is (1:30)~(1:70).

2. The method of claim 1, wherein, The surfactant is cetyltrimethylammonium bromide, and the molar ratio of the surfactant to metal ions is (1:30)~(1:180).

3. The method of claim 1, wherein, The volume of the removed supernatant is 50%-85% of the total volume.

4. The method of claim 1, wherein, The flat hydrophilic substrate is selected from any one of silicon wafer, glass, quartz, stainless steel, aluminum alloy and ceramic.

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